The present invention relates to insulation panel systems. More particularly, it relates to an insulated panel design having improved resistance to warpage due to the thermal strain imparted by exposure of the panel to large temperature differences.
Insulated panel systems for use in freezing or for containing materials at very low temperatures have been practiced in many forms in the art. Such systems can be easily fitted to odd shapes, can be made lightweight, provide easy maintenance, and can be mass produced at low cost. When subjected to large temperature differences, however, thermal strains are developed in the panel envelope and in the internal insulation. These can result in undesired warpage and/or breakage of the panel due to the temperature difference between the top and bottom surfaces thereof.
The problem of insulation panel warpage is significant due to its potential for causing leaks from a freezer or container, damaging or deforming the insulation panels, and damaging or deforming components in the freezer or container that connect to the insulation panels. A good seal of the insulation panel when cold is critical to the proper operation of a freezer. Leaks can allow infiltration of air into the freezer which can affect its efficiency and lead to icing problems. The panels can be permanently deformed or cracked if not designed properly. Typically in a liquid nitrogen food freezer, for example, the insulation panel should have a fully welded construction to prevent oxygen from the air from condensing and concentrating inside the panel and posing a safety problem. Also, damage and cracks on the outside of a panel can allow moisture to enter the panel and cause degradation of the thermal insulation over time. The following patents illustrate various prior approaches to solving such problems.
In U.S. Pat. Nos. 4,116,150 and 4,170,952 to McCown there are disclosed cryogenic insulation systems for the storage of cryogenic liquefied gases which employ a metal membrane formed of a high nickel steel such as Invar.
In U.S. Pat. No. 4,155,482 to Swaney, there is disclosed a modular, bolt on, insulation system for use in the inner cargo hold of liquid natural gas (LNG) tanker ships. The panels are stacked in multiple sealed layers and are made of composites. There is a complicated system of joints and seams to completely cover the inner cargo hold. The modularity allows for replacement of damaged panels and inner vessel maintenance. The panels are not sealing surfaces but are simply applied to the inner vessel to provide thermal insulation between the cold LNG and the ambient environment.
In U.S. Pat. No. 4,527,844 to Klee, there is disclosed a thermally insulated chamber with an insulated door. The design of the chamber walls and door use flexible expansion joints, flexible support members, and limit the inner liner linear dimensions to control buckling and warping.
In U.S. Pat. No. 5,032,439 to Glicksman et. al. there are disclosed thermal insulation panels using evacuated powders enclosed in a ceramic glass envelope which is evacuated to a low pressure. This is a complicated design that was generated to form a panel without using CFC producing closed cell foams.
In U.S. Pat. No. 5,445,857 to Nowobilski, (assigned to the assignee of the present invention) there are described vacuum insulation panels that are provided with textured surfaces that localize thermal expansion. The large thermal strains that can produce cracking and warping are thereby avoided.
In U.S. Pat. No. 5,502,982 to Venetucci, there is disclosed the use of a tie pin to limit the deformation of the panel due to ice build up in the inner metal surfaces. The tie pins hold a plywood inner support next to the inner metal skin and are composed of a low heat leak composite material. Several of the pins are required for each panel. They are said to prevent the deformation of the inner surface of the insulation panel and thereby alleviate problems in a tunnel freezer operation caused by the deformation.
The above patents are specifically incorporated by reference herein.
The designs presented in accordance with this invention are significantly easier and cheaper to fabricate and construct than the prior designs and provide an essentially equivalent degree of thermal insulation. The prior art has tended to solve the problems of buckling and warpage by complicated mechanical means (tie pins or flexible expansion joints). The designs of this invention solve the problems of thermally generated warpage without significant mechanical complexity. The embodiments of this invention which employ Invar, preferably use it only on the portion of the panel which will be exposed to significant temperature variations from ambient temperature, in order to minimize cost.
In accordance with this invention new thermal insulation panel designs are provided having very low warpage when the inside surface of the panel is exposed to temperatures as low as xe2x88x92320xc2x0 F. while the outside of the panel is at ambient temperature. The insulation panels of this invention have a simple modular design that is easy and inexpensive to fabricate.
The thermal insulation panel in accordance with a preferred embodiment of the invention exhibits little or no warping due to temperature differences between different portions of the panel. The panel comprises insulation material and an envelope encapsulating the insulation material. The envelope comprises a base member and a cover member which cooperate to envelope the insulation material. The cover member is supported by the base member in a floating and sealing engagement with the base member. The cover member can slide relative to the base member to compensate for differential thermal expansion effects when the respective base member and cover member are exposed to different temperatures.
Preferably in accordance with one embodiment the base member includes a peripheral slot directed inwardly of the panel and the cover member is captured within the slot and is free to slide in the slot within a given range of motion. In accordance with another embodiment the cover member includes a peripheral slot directed inwardly of the panel and the base member is captured within the slot so that the cover member is free to slide relative to the base member within a given range of motion.
A first sealing member is arranged about a peripheral edge of the cover member or the base member to provide a seal between the respective cover member or base member and the slot. Preferably the cover member and the base member are formed of metal and the first sealing member comprises a polymer.
In accordance with further preferred embodiments of this invention there is provided a thermal insulation panel which exhibits little or no warping due to temperature differences between different portions of the panel. The panel comprises insulation material and an envelope for encapsulating the insulation material. The envelope comprises a base member and a cover member. The cover member is adapted to be exposed to a temperature significantly below the temperature to which the base member is exposed. The cover member is formed of a metal having a low coefficient of thermal expansion to compensate for differential thermal expansion effects in the respective base member and cover member. The cover member and the base member are joined in a manner which provides the envelope with a hermetic seal.
Preferably the cover member and the base member are welded together along a peripheral seam of the panel. Preferably the seam is arranged away from the low temperature exposed portion of the panel.
It is therefore an object of the present invention to provide an improved insulation panel having resistance to warping due to differential thermal expansion effects (i.e. due to the effect upon different portions of the panel being exposed to different temperatures).
It is another object of the present invention to provide an insulation panel as above which is easy to fabricate.
It is another object of one alternative of the present invention to provide an insulation panel as above which includes a sliding seal to inhibit moisture infiltration into the panel.
It is another object of another alternative of the present invention to provide an insulation panel as above which includes a hermetically sealed envelope to prevent moisture infiltration into the panel.
The above and further objects and advantages of this invention will become apparent upon consideration of the following description thereof.